Conventional indole-3-acetic acid (IAA) and derivatives thereof (methyl indole-3-acetate, indole-3-acetamide, etc.) are disadvantageous in that the carbon atoms at the 2- and 3-positions of indole ring are highly reactive, so that in living plants, these compounds are oxidized, are liable to be decomposed, and disappear in the living plants before they can exhibit their plant-growing action sufficiently.
In addition, 4,7-dichloroindole-3-acetic acid, 5,7-dichloroindole-3-acetic acid, etc. are known in Planta 140, 89 (1978). Therein, it is described that dichloroindole-3-acetic acid above has anti-auxin action, but there is given no description of its ability to promote plant growth.